1. Field of the Invention
The present invention relates to systems and methods that are used to separate molecular hydrogen from a volume of gas. More particularly, the present invention is related to systems and methods that separate hydrogen from a volume of mixed gas and utilize the hydrogen as fuel for a fuel cell.
2. Prior Art Description
In industry, there are many applications for the use of ultra pure molecular hydrogen. For instance, there are many fuel cells that operate using hydrogen. The hydrogen, however, must be ultra pure. Any molecules of carbon dioxide, carbon monoxide or other contaminant gases that are received by the fuel cell either reduces its efficiency or causes damage to the fuel cell.
Hydrogen gas does not exist naturally on earth to any significant extent because it reacts with many elements and readily combines to form compounds. Hydrogen gas must therefore be manufactured. Hydrogen gas can be manufactured in a number of ways. For instance, hydrogen gas can be created by splitting water molecules through electrolysis. However, the power needed for electrolysis is always greater than the powered available from a fuel cell that utilizes the output hydrogen gas from the electrolysis. Any fuel cell system that obtains hydrogen gas from electrolysis therefore results in a net power loss.
Most commonly, the purified hydrogen that is used by a fuel cell is generated by obtaining hydrogen gas from a hydrocarbon, using a multi-stage process. In industry, hydrogen gas is most often obtained by breaking down either fossil or biofuels, both of which are in the general class of hydrocarbons. In a first stage, a hydrocarbon such as gasoline, methane, diesel or other hydrocarbons which have the form CnH(2n+2) is broken down to less complex molecules. When such hydrocarbons are broken down, hydrogen gas is liberated from the hydrocarbon. The breaking down the hydrocarbons to generate hydrogen has been done for approximately 100 years. During this time frame the general process has remained the same and it is based on equilibrium reactions. The general process for breaking down hydrocarbons involves a high temperature cracking of the hydrocarbon fuel, a lower temperature water gas shift reaction to increase the concentration of hydrogen and then a separation of the hydrogen. The hydrogen must then be purified in a secondary process to achieve the desired level of purity. Such prior art industrial processes typically require millions of dollars in equipment and building sized facilities. It is therefore expensive to create extremely pure hydrogen gas. Accordingly, if hydrogen gas is used as a direct source of energy, it is one of the most uneconomical fuels that can be used without the invention described in this patent application.
One of the few places that hydrogen gas is used as a fuel is in a proton exchange membrane (PEM) fuel cell. A PEM fuel cell only utilizes hydrogen gas that has been processed to extreme levels of purity. In many common processes that produce hydrogen, the hydrogen gas produced by that process is not pure enough to be used directly by the PEM fuel cell. Rather, when hydrogen is produced, the resultant gas is often contaminated with water vapor, hydrocarbons and/or other contaminants. It is for this reason that once hydrogen gas is generated, it must be purified in a second processing stage. The cost of this processing depends on the level of purity required. The purer the hydrogen gas, the greater the time, money and energy are required.
In the art, ultra pure hydrogen is commonly considered to be hydrogen having purity levels of at least 99.999%. In the prior art, one of the most common ways to purify contaminated hydrogen gas is to pass the gas through a conduit made of a hydrogen permeable material, such as palladium or a palladium alloy. As the contaminated hydrogen gas passes through the conduit, atomic hydrogen permeates through the walls of the conduit, thereby separating from the contaminants. In such prior art processes, the conduit is kept internally pressurized and is typically heated to at least three hundred degrees centigrade. Within the conduit, molecular hydrogen disassociates into atomic hydrogen on the surface of the conduit and the conduit absorbs the atomic hydrogen. The atomic hydrogen permeates through the conduit from a high pressure side of the conduit to a low pressure side of the conduit. Once at the low pressure side of the conduit, the atomic hydrogen recombines to form molecular hydrogen. The molecular hydrogen that passes through the walls of the conduit can then be collected for use. Such prior art systems are exemplified by U.S. Pat. No. 5,614,001 to Kosaka et al., entitled Hydrogen Separator, Hydrogen Separating Apparatus And Method For Manufacturing Hydrogen Separator.
In the past, fuel cells have mostly been used to power exotic devices, such as spacecraft. Accordingly, the cost of operating a two stage system for obtaining purified hydrogen is of little concern. However, if fuel cells are to be used to power more traditional devices, such as automobiles, cost is one of the most important design criteria. It is primarily the cost associated with using hydrogen that have prevented fuel cell technology from spreading into traditional consumer products.
Consider an automobile. In order to use a fuel cell in an automobile, hydrogen gas would have to be separated from a source gas at some processing plant. The hydrogen gas would then be purified in an expensive secondary process. The purified hydrogen, as a gas or liquid, would then be shipped under some pressure to gas stations for storage. The high pressure hydrogen would then have to be pumped at even high pressures into the automobile for storage. Within the automobile, the high pressure hydrogen would then have to be dropped to near atmospheric levels prior to its use by the fuel cell. This fueling scenario requires pressurized tanks to be maintained both at the gas station and within the automobile. It also requires pumping lines and couplings for fueling the automobile that can hold hydrogen gas under immense pressure. The dangers and cost of refueling alone have long been deterrents to producing any vehicle that runs on hydrogen.
A long-standing need, therefore, exists for an integrated compact fuel processing system, wherein a traditional fuel, such as diesel or gasoline, can be pumped into the gas tank of an automobile or a ship in the ordinary manner. A fuel processing system carried within the automobile or ship will then obtain ultra pure hydrogen from that traditional fuel using an integrated process that operates on an as-needed basis. The ultra pure hydrogen can then be used to power a fuel cell for the production of electricity.
This need is met by the present invention as described and claimed below.